• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.13-23
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• 1997

액체 로켓 추진기관의 개발에 가장 큰 장애요인은 연소불안정 현상이다. 연소불안정이 생기는 원인과 연소실내 음향효과에 따른 분류를 행하고 액체 로켓 추진기관 개발에서 발생하였던 연소 불안정 현상을 추진제 종류와 특성에 따라 살펴보았다. 또한 추진기관의 연소 안정성을 보장하기 위한 성능확인 시험과 연소 불안정을 억제하는 능동적, 수동적 방법에 관하여 기술하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.431-432
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• 2014

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12C
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• pp.1035-1043
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• 2010

This paper presents a listening angle estimation scheme based on received signal power difference (RSPD) using acoustic signals, and analyzes the performance of the proposed scheme. The RSPD as the measurement to estimate the listening angle is considered for the first time in this paper. We mathematically analyze the error characteristics of the proposed scheme and present the characteristics of the proposed scheme through the Monte-Carlo simulation. We also conduct actual experiments in an anechoic room to evaluate the performance of the proposed scheme to compare with the conventional scheme.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.445-450
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• 1999

확산(Diffusion)은 실의 음향성능에 있어서 중요한 요소이나 확산성을 측정하기가 기술적으로 어렵고 실 표면에서의 확산정도도 계량하기가 어렸운것이 현실이다. 이에 본 연구의 목적은 현장실험을 통하여 표면의 확산성을 측정할 수 있는 새로운인자(가칭:${\Delta}x$)의 가능성을 개진하는 것이다. 실험결과에 의하면 확산성이 높은 홀에서 두개의 마이크로폰에 의하여 측정된 ${\Delta}x$의 값은 확산성이 높은 홀이 낮은 홀에서 보다 평균적으로 작은 값이 나왔다. 이것은 확산이 잘 이루어지는 홀에서는 각 방향으로의 음이 고루 분포하여 객석에 도달하고 있다는 것을 나타낸다. 즉 음이 각 방향으로 고루 전달되고 있다는 것을 나타낸다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.18-21
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• 2008

Acoustic design parameters of a half-wave resonator are studied experimentally for acoustic stability in a model combustor. According to standard acoustic-test procedures, acoustic-pressure signals are measured. Quantitative acoustic properties of damping factor and sound absorption coefficient are evaluated and thereby, the acoustic damping capacity of the resonator is characterized. The diameter and the number of a half-wave resonator, its distribution are selected as design parameters for optimal tuning of the resonator. Acoustic damping capacity increases as the resonators with diameter increases. The optimum number of resonators or the optimum open-area ratio decreases as boundary absorption decreases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.130-137
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• 2010

An uplink indoor positioning system is proposed in the present work, where the acoustic signals are solely used for positioning. The underlying acoustic signals include whistle, finger snap, and hands-clapping. In the proposed method, positioning is achieved by finding the time-difference-of-arrivals using several self-generating sounds. To evaluate the feasibility of the signals and their positioning accuracies, the database of 100 persons about self-generating acoustic signals is built up. The results show that the hands-clapping sound is the most suitable for acoustic-based indoor positioning.

• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.87-94
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• 2009

Recently, in accordance with the interesting on well-being as well as the revitalization of living athletics, it is current tendency that people who use the swimming pools are on increasing. However, because the most of indoor swimming pools have ever used the reflection finishing materials likely as the tile due to the property of its hydrophilic space, the inside of indoor swimming pool is vibrating too much, and some problem which the voice and music do not delivering clearly is occurring when swimming lessons or underwater aerobics(synchronized swimming) and swimming game. Based on such viewpoint, locating the object on actually built indoor swimming pool, this Study has ever grasped its physical acoustic property, and finally designed the indoor swimming pool that contains an optimum acoustic condition, by remodelling it through an acoustic simulation. It is considered that such study result could be utilized as the useful materials when constructing the similar indoor swimming pool, hereafter.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• The Journal of the Acoustical Society of Korea
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• v.11 no.2
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• pp.50-58
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• 1992

To improve the quality of dwelling environment of domestic apartment house, it is required to establish the sound insulation standard and the performance evaluation method which is suitable to the domestic residential conditions. In this study, the properties of internal noisy sources of a single unit in apartment houses and the sound insulation performance of party walls are investigated and analyzed, as a primary step to the establishment of sound insulation standard. Based on these data, the differences in sound insulation index of each plane type are investigated along with their causes. Also, the factor which affect and decide the insulation performance are analyzed in an effort to improve the performance of party wall structures.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.497-503
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• 2010

In this paper, evaluation of noise reduction performance of HVAC system for ships by means of HVAC mock-up system is presented. Test is done for six different types of HVAC elements including room unit, silencer, etc. It is found that when diameter of silencer is small and air flow is large, flow noise degrades insertion loss. However, as diameter of silencer becomes larger, the effect of flow noise becomes smaller, and insertion loss up to 25 dB is measured. It is observed that insertion loss of diffuser type room unit is usually between zero and 10 dB, whereas that of the nozzle type room unit can be down to - 15 dB. In addition, it is shown that changing duct arrangement can reduce cabin noise by up to 2 dB, and providing same air flow to each room unit is crucial for generating less noise.